The present invention relates generally to water electrolyzers and relates more particularly to a universal cell frame for a high-pressure (about 200 to 12,000 psi) water electrolyzer and to a water electrolyzer including said universal cell frame.
Water electrolysis is an important process for producing hydrogen, especially at remote sites, for electric generator cooling, materials processing, chemical reactions and laboratory use and analysis. Also, when low-cost power is available from renewable energy sources (e.g., wind, solar), water electrolyzers can cost-effectively and efficiently provide hydrogen, as an alternative to fossil fuels, for stationary and vehicular power applications.
Currently, two different water electrolysis technologies compete in the marketplace. The first and most developed technology is alkaline water electrolysis, in which the stack and cell electrolyte is liquid potassium hydroxide (KOH). The second technology is polymer electrolyte membrane (PEM) water electrolysis technology, which uses a solid proton-conductive membrane as the sole electrolyte in the system. PEM systems have significant advantages over alkaline electrolyzer systems for lightweight or high-pressure breathing or life-support applications, such as on board spacecraft and nuclear submarines. Some of the advantages of a PEM system include (1) superior performance at a given current density, (2) reliability (over 100,000 hours of highly invariant performance), (3) operational safety benefits of deionized-water system over a highly caustic system, and (4) a PEM system can effectively operate at high differential pressures of over 3,000 psi while liquid electrolyte alkaline systems are limited to differential pressures of inches of water.
In a typical PEM water electrolyzer, an anode is positioned along one face of a polymer electrolyte membrane, and a cathode is positioned along the opposite face of the polymer electrolyte membrane. To enhance electrolysis, a catalyst, such as platinum, is typically present both at the interface between the anode and the polymer electrolyte membrane and at the interface between the cathode and the polymer electrolyte membrane. The above-described combination of a polymer electrolyte membrane, an anode, a cathode and associated catalysts is commonly referred to in the art as a membrane electrode assembly.
In use, water is delivered to the anode and an electric potential is applied across the two electrodes, thereby causing the electrolyzed water molecules to be converted into protons, electrons and oxygen atoms. The protons migrate through the polymer electrolyte membrane and are reduced at the cathode to form molecular hydrogen. The oxygen atoms do not traverse the polymer electrolyte membrane and, instead, form molecular oxygen at the anode.
Often, a number of electrolysis cells are assembled together in order to meet hydrogen or oxygen production requirements. One common type of assembly is a stack comprising a plurality of stacked electrolysis cells that are electrically connected in series in a bipolar configuration. In one type of stack, each cell includes, in addition to a membrane electrode assembly of the type described above, a pair of multi-layer metal screens, one of said screens being in contact with the outer face of the anode and the other of said screens being in contact with the outer face of the cathode. The screens are used to conduct electrons to and from the cathode and anode and to form the membrane-supporting fluid cavities within a cell for the flow of water, hydrogen and oxygen. Each cell typically additionally includes a pair of polysulfone cell frames, each cell frame peripherally surrounding a set of screens. The frames are used to peripherally contain the fluids and to conduct the fluids into and out of the screen cavities. Each cell typically further includes a pair of metal foil separators, one of said separators being positioned against the outer face of the anode screen and the other of said separators being positioned against the outer face of the cathode screen. The separators serve to axially contain the fluids on the active areas of the cell assembly. In addition, the separators and screens together serve to conduct electricity from the anode of one cell to the cathode of its adjacent cell. Plastic gaskets may be used to seal the outer faces of the cell frames to the metal separators, the inner faces of the cell frames being sealed to the proton exchange membrane. The cells of the stack are typically compressed between a spring-loaded rigid top end plate and a bottom base plate. Electrically-conductive compression pads may be positioned between adjacent cells in a stack in order to maintain uniform contact pressure over the entire active areas of the electrodes.
Patents and publications relating generally to electrolysis cell stacks include the following, all of which are incorporated herein by reference: U.S. Pat. No. 7,438,985, inventors LaConti et al., issued Oct. 21, 2008; U.S. Pat. No. 7,261,967, inventors LaConti et al., issued Aug. 28, 2007; U.S. Pat. No. 7,229,534, inventors LaConti et al., issued Jun. 12, 2007; U.S. Pat. No. 6,685,821, inventors Kosek et al., issued Feb. 3, 2004; U.S. Pat. No. 6,500,319, inventors LaConti et al., issued Dec. 31, 2002; U.S. Pat. No. 6,057,053, inventor Gibb, issued May 2, 2000; U.S. Pat. No. 5,350,496, inventors Smith et al., issued Sep. 27, 1994; U.S. Pat. No. 5,316,644, inventors Titterington et al., issued May 31, 1994; U.S. Pat. No. 5,009,968, inventors Guthrie et al., issued Apr. 23, 1991; and Coker et al., “Industrial and Government Applications of SPE Fuel Cell and Electrolyzers,” presented at The Case Western Symposium on “Membranes and Ionic and Electronic Conducting Polymer,” May 17-19, 1982 (Cleveland, Ohio).
As noted above, cell frames are often utilized in electrolysis cells to conduct and to contain the cell operating fluids. Such cell frames are typically made of plastics like polysulfones that offer the advantages of chemical inertness and electrical resistance that are desirable and necessary in these cells.
Referring now to FIG. 1, there is shown a partially-exploded perspective view of a conventional PEM water electrolyzer (i.e., electrolysis cell), said conventional PEM water electrolyzer being represented generally by reference numeral 11. For the sake of simplicity, certain aspects of conventional PEM water electrolyzer 11 are neither shown nor discussed herein.
Electrolyzer 11 comprises a membrane electrode assembly 12, membrane electrode assembly 12 comprising a polymer electrolyte membrane (PEM) 13, an anode 14 positioned along one face of PEM 13, and a cathode 15 positioned along the opposite face of PEM 13. Electrolyzer 11 further comprises an anode screen 16 in contact with the outer face of anode 14, a cathode screen 17 in contact with the outer face of cathode 15, an anode separator 18 positioned against the outer face of anode screen 16, a cathode separator 19 positioned against the outer face of cathode screen 17, an anode frame 20, a cathode frame 21, an anode gasket 22, and a cathode gasket 23.
Anode frame 20, which is also shown separately in FIG. 2, comprises a unitary annular member 25, member 25 comprising an inner surface 27, an outer surface 29, a top surface 31, and a bottom surface 33. A pair of closely-spaced, substantially elliptical, transverse openings 35-1 and 35-2 are provided in member 25, each of openings 35-1 and 35-2 extending transversely from top surface 31 to bottom surface 33. In addition, a plurality of closely-spaced, substantially elliptical, transverse openings 35-3, 35-4 and 35-5 are provided in member 25, each of openings 35-3 through 35-5 extending transversely from top surface 31 to bottom surface 33. Openings 35-3, 35-4 and 35-5 are positioned in a substantially diametrically-opposed manner relative to openings 35-1 and 35-2, i.e., openings 35-3, 35-4 and 35-5 are positioned approximately 180 degrees away from openings 35-1 and 35-2. A plurality of radial passageways 37 are provided in member 25, each radial passageway 37 extending radially outwardly from inner surface 27 into fluid communication with one of openings 35-1 through 35-5. As shown, each of openings 35-1 through 35-5 has seven passageways 37 associated therewith.
A pair of substantially circular, transverse openings 39-1 and 39-2 are provided in member 25, each of openings 39-1 and 39-2 extending transversely from top surface 31 to bottom surface 33. Transverse openings 39-1 and 39-2 are positioned approximately 180 degrees away from one another. In addition, each of transverse openings 39-1 and 39-2 is positioned approximately 90 degrees away from openings 35-1 and 35-2 and approximately 90 degrees away from openings 35-3 through 35-5.
A pair of substantially circular, transverse openings 41-1 and 41-2 are provided in member 25, each of openings 41-1 and 41-2 extending transversely from top surface 31 to bottom surface 33. Openings 41-1 and 41-2 may be used to receive rods or similar hardware (not shown) to compress a plurality of electrolyzers 11 between a pair of plates (not shown).
A plurality of circumferential sealing ribs 51 for sealing with anode gasket 22 are provided on top surface 31 of member 25, ribs 51 being concentrically arranged in the space between inner surface 27 and openings 35-1 through 35-5, openings 39-1 and 39-2, and openings 41-1 and 41-2. Additional pluralities of concentric ribs for sealing with gasket 22 are provided on top surface 31 of member 25, said ribs consisting of ribs 53 surrounding opening 39-1, ribs 55 surrounding opening 39-2, ribs 57 surrounding both opening 35-1 and opening 35-2, and ribs 59 surrounding all three of openings 35-3 through 35-5. Corresponding pluralities of sealing ribs (not shown) are provided on bottom surface 33 of member 25.
Cathode frame 21, which is also shown separately in FIG. 3, comprises a unitary annular member 65, member 65 comprising an inner surface 67, an outer surface 69, a top surface 71, and a bottom surface 73. A pair of closely-spaced, substantially elliptical, transverse openings 75-1 and 75-2 are provided in member 65, each of openings 75-1 and 75-2 extending transversely from top surface 71 to bottom surface 73. In addition, a plurality of closely-spaced, substantially elliptical, transverse openings 75-3, 75-4 and 75-5 are provided in member 65, each of openings 75-3 through 75-5 extending transversely from top surface 71 to bottom surface 73. Openings 75-3, 75-4 and 75-5 are positioned in a substantially diametrically-opposed manner relative to openings 75-1 and 75-2, i.e., openings 75-3, 75-4 and 75-5 are positioned approximately 180 degrees away from openings 75-1 and 75-2.
A pair of substantially circular, transverse openings 79-1 and 79-2 are provided in member 65, each of openings 79-1 and 79-2 extending transversely from top surface 71 to bottom surface 73. Transverse openings 79-1 and 79-2 are positioned approximately 180 degrees away from one another. In addition, each of transverse openings 79-1 and 79-2 is positioned approximately 90 degrees away from openings 75-1 and 75-2 and approximately 90 degrees away from openings 75-3 through 75-5. A plurality of radial passageways 78 are provided in member 65, each radial passageway 78 extending radially outwardly from inner surface 67 into fluid communication with one of openings 79-1 and 79-2. As shown, each of openings 79-1 and 79-2 has four passageways 78 associated therewith.
A pair of substantially circular, transverse openings 81-1 and 81-2 are provided in member 65, each of openings 81-1 and 81-2 extending transversely from top surface 71 to bottom surface 73. Openings 81-1 and 81-2 may be used to receive bolts or similar hardware (not shown) to compress a plurality of electrolyzers 11 between a pair of plates (not shown).
A plurality of circumferential sealing ribs 91 for sealing with cathode gasket 23 are provided on bottom surface 73 of member 65, ribs 91 being concentrically arranged in the space between inner surface 67 and openings 75-1 through 75-5, openings 79-1 and 79-2, and openings 81-1 and 81-2. Additional pluralities of concentric ribs for sealing with gasket 23 are provided on bottom surface 73 of member 65, said ribs consisting of ribs 93 surrounding opening 79-1, ribs 95 surrounding opening 79-2, ribs 97 surrounding both opening 75-1 and opening 75-2, and ribs 99 surrounding all three of openings 75-3 through 75-5. Corresponding pluralities of sealing ribs (not shown) are provided on top surface 71 of member 65.
Anode frame 20 and cathode frame 21 have matching sizes and shapes are oriented relative to one another so that openings 35-1 and 35-2 of anode frame 20 are aligned with openings 75-1 and 75-2, respectively, of cathode frame 21, so that openings 35-3 through 35-5 of anode frame 20 are aligned with openings 75-3 through 75-5, respectively, of cathode frame 21, so that openings 39-1 and 39-2 of anode frame 20 are aligned with openings 79-1 and 79-2, respectively, of cathode frame 21, and so that openings 41-1 and 41-2 of anode frame 20 are aligned with openings 81-1 and 81-2, respectively, of cathode frame 21. This arrangement is repeated where a plurality of electrolyzers 11 are combined in a bipolar stack. In this manner, openings 35-1 through 35-5, openings 75-1 through 75-5, openings 39-1 and 39-2, and openings 79-1 and 79-2 serve as axial ports to fluidly interconnect a number of electrolyzers 11.
In those instances when electrolyzer 11 is operated under anode feed conditions, water is supplied to openings 35-1 and 35-2 of anode frame 20, where at least a portion of said water is conducted from openings 35-1 and 35-2 through radial passageways 37 to the anode side of membrane electrode assembly 12. The oxygen gas produced on the anode side of membrane electrode assembly 12, together with excess water, is conducted away from membrane electrode assembly 12 through radial passageways 37 leading to openings 35-3 through 35-5 of anode frame 20. The hydrogen gas produced on the cathode side of membrane electrode assembly 12 is conducted away from membrane electrode assembly 12 through radial passageways 78 leading to openings 79-1 and 79-2. On the other hand, where electrolyzer 11 is operated under cathode feed conditions, water is supplied to opening 79-1 of cathode frame 21, where at least a portion of said water is conducted from opening 79-1 through radial passageways 78 to the cathode side of membrane electrode assembly 12. The hydrogen gas produced on the cathode side of membrane electrode assembly 12, together with excess water, is conducted away from membrane electrode assembly 12 through radial passageways 78 leading to opening 79-2 of cathode frame 22. The oxygen gas produced on the anode side of membrane electrode assembly 12 is conducted away from membrane electrode assembly 12 through radial passageways 37 leading to openings 35-1 through 35-5.
As can be appreciated, because electrolyzer 11 is designed for anode flow, the number of passageways in anode frame 20 is tailored to match gas and water flow to control pressure drop within anode frame 20. However, when coolant flow is moved to the cathode side, more water will pass through a smaller number of ports and will result in a high pressure drop in the frame porting region of the coolant loop.